WO2012172945A1

WO2012172945A1 - Exhaust gas after-treatment device

Info

Publication number: WO2012172945A1
Application number: PCT/JP2012/063195
Authority: WO
Inventors: 真範八田; 昭一前田; 笹谷　亨; 信太郎川崎; 敦城所; 作太郎星
Original assignee: 株式会社豊田自動織機
Priority date: 2011-06-15
Filing date: 2012-05-23
Publication date: 2012-12-20

Abstract

Downstream of a curved section (2a) of an exhaust gas pipe (2) is provided an SCR catalyst (4) which, with urea water injected from an injection nozzle (5) as a reducing agent, purifies NO_X contained in an exhaust gas. Further, between the curved section (2a) and the SCR catalyst (4) are provided dispersion members (21-23) for dispersing in the exhaust gas pipe (2) the urea water injected from the injection nozzle (5), and a mixer (31) for mixing the dispersed urea water into the exhaust gas. The injection nozzle (5) is positioned upstream of the dispersion members (21-23) and arranged on the outer circumference side of the curved section (2a) so that the injected urea water can impinge directly on the surfaces (21a-23a) of the dispersion members (21-23).

Description

Exhaust gas aftertreatment device

This invention relates to an exhaust gas aftertreatment device, and more particularly to a configuration for purifying exhaust gas of a diesel engine using a reducing agent and a reduction catalyst.

An example of an exhaust gas aftertreatment device that purifies exhaust gas of a diesel engine is a urea selective reduction system (urea SCR system) that purifies nitrogen oxide (NOx) in exhaust gas using urea water as a reducing agent. For example, as described in Patent Document 1, the urea SCR system includes a reduction catalyst provided in the exhaust pipe and a reducing agent injection device that injects urea water into the exhaust pipe on the upstream side of the reduction catalyst. . The reduction catalyst reacts ammonia (NH ₃ ) generated from urea water injected into the exhaust pipe with NOx contained in the exhaust gas, and reduces it to harmless nitrogen (N ₂ ) and water (H ₂ O). To do. In order to perform this reduction efficiently, it is necessary to supply urea water with a uniform distribution to the reduction catalyst.

Also, the urea SCR system described in Patent Document 1 includes a mixer unit for mixing exhaust gas and urea water to make the distribution state of urea water uniform. The mixer unit is a plate-like member provided between the reducing agent injection device and the reduction catalyst, and includes a plurality of passages through which exhaust gas and urea water flow, and a plurality of passages formed on the outlet side of each passage. With fins. The reducing agent injection device injects urea water toward the mixer plate, and the urea water atomized by colliding with the mixer plate is dispersed in the exhaust pipe. The dispersed urea water passes through each passage of the mixer plate together with the exhaust gas, and then is mixed with the exhaust gas by the turbulent flow generated by each fin and then supplied to the reduction catalyst.

JP 2009-24654 A

In order to uniformly disperse the urea water with the mixer plate described in Patent Document 1, it is necessary to cause the urea water injected from the reducing agent injection device to collide with the entire surface of the mixer unit. Here, the reducing agent injection device normally injects urea water in a conical shape. Therefore, in order for the urea water to collide with the entire surface of the mixer unit, it is necessary to provide a distance between the reducing agent injection device and the mixer unit so that the injection range of the urea water is sufficiently widened. That is, the urea SCR system described in Patent Document 1 has a problem that the exhaust pipe on the upstream side of the mixer unit cannot be shortened and it is difficult to downsize the entire apparatus.

In general, the exhaust pipe is generally curved at a plurality of locations such as the upstream side of the reduction catalyst due to a layout problem when mounted on the vehicle. In such a case, in the urea SCR system described in Patent Document 1, there may be a case where a desired distance cannot be taken between the reducing agent injection device and the mixer unit in order to widen the injection range of the urea water. That is, when the exhaust pipe includes a curved portion on the upstream side of the mixer unit, the urea SCR system described in Patent Document 1 cannot make urea water collide with the entire surface of the mixer unit, and the urea water is uniformly dispersed. It had the problem that it became difficult to do.

The present invention has been made to solve such a problem, and the exhaust gas after realizing the downsizing while uniformly distributing the reducing agent to the exhaust gas in the exhaust pipe including the curved portion is realized. An object is to provide a processing apparatus.

An exhaust gas aftertreatment device according to the present invention has an exhaust pipe having a curved portion that bends the direction in which exhaust gas flows, and exhaust gas discharged from an internal combustion engine, and a reducing agent is injected into the exhaust pipe. An exhaust gas after-treatment device comprising: a reducing agent supply device for reducing the exhaust gas by reacting the exhaust gas with the reducing agent, disposed on the downstream side of the reducing agent supply device and the curved portion. The plate-shaped dispersion member disposed between the curved portion and the reduction catalyst, and having one surface facing the outer peripheral side of the curved portion, and disposed between the dispersion member and the reduction catalyst, and the exhaust gas And a mixing means for mixing the reducing agent with the reducing agent, and the reducing agent injection device is disposed at a portion upstream of the dispersion member and at a portion where the reducing agent can be injected toward one surface of the dispersion member. The

The dispersing member and the mixing means may be arranged adjacent to each other. Here, the term “adjacent” means that not only the dispersion member and the mixing means are integrally formed, but also separate parts that are substantially separated within a range where the exhaust gas flow does not change between the dispersion member and the mixing means. Including, for example, those separated by a distance of 10% or less with respect to the diameter of the exhaust pipe.

When the exhaust pipe extends straight and has a straight piping part between the curved part and the reduction catalyst in which the dispersing member and the mixing means are arranged, the dispersing member extends in parallel to the axial direction of the straight piping part. be able to. Here, the term “parallel” does not need to be strictly parallel, and includes an angle at which pressure loss is negligible. Also, a plurality of dispersing members can be provided.

The mixing means has a plurality of first fins and a plurality of second fins which are arranged so as to be parallel to each other and which incline the flow of exhaust gas passing therethrough at a predetermined angle which is opposite to each other. The mixing means and the reduction catalyst are sequentially connected through a part of the straight piping portion and a tapered piping portion formed so as to widen from the upstream side to the downstream side. In this case, when the angle is α, the inner diameter of the straight piping portion is D, and the length of the straight piping portion from the mixing means to the tapered piping portion is L,
D / 2 × cotα ≦ L ≦ 3/2 × D × cotα
Meet.

In the mixing means, a row in which a plurality of first fins are arranged and a row in which a plurality of second fins are arranged are alternately arranged one by one. Moreover, the straight piping part can be made into a cylindrical shape. Furthermore, the gradient at which the tapered pipe portion spreads can be made smaller than the angle α, and the angle α can be set to 45 °.

According to the present invention, in an exhaust gas aftertreatment device having an exhaust pipe including a curved portion, it is possible to reduce the size of the exhaust gas while uniformly dispersing the reducing agent in the exhaust gas.

It is the schematic which shows the structure of the exhaust-gas aftertreatment apparatus which concerns on Embodiment 1 of this invention. 2 is a cross-sectional view schematically showing a configuration of a main part in the exhaust gas aftertreatment device according to Embodiment 1. FIG. FIG. 2 is a perspective view schematically showing a dispersion member and mixing means in the exhaust gas aftertreatment device according to Embodiment 1, wherein (a) is a perspective view seen from the downstream side in the exhaust gas flow direction, and (b) is an upstream side. It is the perspective view seen from the side. FIG. 4 is a cross-sectional view taken along IV-IV in FIG. 2. FIG. 3 is a schematic diagram for explaining the flow of exhaust gas in the exhaust gas aftertreatment device according to Embodiment 1; It is a cross-sectional side view which shows roughly the structure of the exhaust-gas aftertreatment apparatus which concerns on Embodiment 2 of this invention. FIG. 6 is a schematic diagram for explaining a flow of exhaust gas generated in a straight pipe section in an exhaust gas aftertreatment device according to Embodiment 2. FIG. 6 is a schematic diagram for explaining a flow of exhaust gas generated inside a straight piping portion and a tapered piping portion in an exhaust gas aftertreatment device according to Embodiment 2. It is a graph which shows transition of the CV value at the time of changing the length of a straight piping part about the exhaust gas aftertreatment device concerning Embodiment 2.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1 FIG.
FIG. 1 schematically shows the configuration of an exhaust system of a diesel engine provided with the exhaust gas aftertreatment device according to the first embodiment.
An exhaust pipe 2 is connected to a diesel engine 1 that is an internal combustion engine, and exhaust gas discharged from the diesel engine 1 circulates inside the exhaust pipe 2 with the diesel engine 1 side as an upstream side. An oxidation catalyst 3 that oxidizes carbon monoxide (CO), hydrocarbon (HC), and the like contained in the exhaust gas is provided in the middle of the exhaust pipe 2. An SCR catalyst 4 that is a reduction catalyst for purifying nitrogen oxide (NOx) contained in the exhaust gas is provided on the downstream side of the oxidation catalyst 3.

The SCR catalyst 4 is a catalyst that purifies NOx by reacting ammonia (NH ₃ ) generated from urea water, which is a reducing agent added to the exhaust gas, and the exhaust gas. Between the oxidation catalyst 3 and the SCR catalyst 4, an injection nozzle 5 is provided as a reducing agent supply device that injects urea water into the exhaust pipe 2. A urea water tank 6 that stores urea water therein and a urea water addition system 7 that supplies urea water in the urea water tank 6 to the injection nozzle 5 are connected to the injection nozzle 5 via a connection pipe 8. ing. The urea water addition system 7 is electrically connected to an ECU 9 that controls the operation of the diesel engine 1 and the exhaust gas aftertreatment device.

An NOx sensor 11 and a NOx sensor 12 for detecting the amount of NOx contained in the exhaust gas are provided on the upstream side and the downstream side of the SCR catalyst 4, and these

NOx sensors

11 and 12 are electrically connected to the ECU 9. Has been. The ECU 9 determines the urea water injection amount and the injection timing based on the NOx amounts detected by the

NOx sensors

11 and 12, and outputs a signal based on the urea water injection system 7 to the urea water addition system 7. Control the injection. Although not shown, on the downstream side of the SCR catalyst 4, a filter that collects particulate matter (PM) contained in the exhaust gas, and a slip that removes ammonia that has passed through the SCR catalyst 4 without being reacted. A catalyst, a muffler for reducing exhaust noise, and the like are sequentially connected.

Here, the exhaust pipe 2 is curved at a plurality of locations due to layout problems when mounted on a vehicle (not shown), and has a curved portion 2 a between the oxidation catalyst 3 and the SCR catalyst 4. More specifically, the exhaust pipe 2 is tapered from the oxidation catalyst 3 toward the downstream side, then curved at the curved portion 2a, and then linearly extending the straight piping portion 2b and the tapered piping portion. 2c is connected to the SCR catalyst 4 sequentially. That is, after the exhaust gas discharged from the diesel engine 1 passes through the SCR catalyst 4, the flow direction is bent by the curved portion 2a, and then passes through the straight piping portion 2b and the tapered piping portion 2c in sequence. The catalyst 4 is supplied. FIG. 1 is a view of the exhaust pipe 2 as viewed from the upper side in the vertical direction, and shows the exhaust pipe 2 being bent in the lateral direction. The exhaust pipe 2 is in any direction other than the lateral direction. Can be curved.

In the exhaust system of the diesel engine 1 configured as described above, urea water injected from the injection nozzle 5 is disposed inside the straight pipe portion 2b located between the curved portion 2a of the exhaust pipe 2 and the SCR catalyst 4. Are provided with three dispersing members 21 to 23 for atomizing and dispersing in the exhaust pipe 2, and a mixer 31 as a mixing means for mixing the urea water dispersed by the dispersing members 21 to 23 into the exhaust gas. It has been. Hereinafter, the dispersive members 21 to 23, the mixer 31, and the configuration around them will be described in detail with reference to FIGS. For convenience of the following description, the left-right direction in the exhaust gas aftertreatment device and the outer peripheral side and inner peripheral side in the curved portion 2a of the exhaust pipe 2 are defined by the arrows shown in FIG.

As shown in FIG. 2, the dispersion members 21 to 23 are flat plate members arranged in the left-right direction inside the straight pipe portion 2b, and extend in parallel along the axial direction of the straight pipe portion 2b. It is provided as follows. Further, the lengths of the dispersion members 21 to 23 along the axial direction of the straight pipe portion 2b are different from each other, and from the dispersion member 21 on the right side toward the dispersion member 23 on the left side, that is, on the outer peripheral side of the curved portion 2a. In other words, the distance from the dispersive member 21 to the dispersive member 23 on the inner peripheral side is further increased as the distance from the injection nozzle 5 increases.

Furthermore, the dispersing members 21 to 23 are provided so that the surfaces 21a to 23a, which are one of these surfaces, face the outer peripheral side of the curved portion 2a. Further, the injection nozzle 5 is disposed immediately before the curved portion 2a, that is, a portion upstream of the dispersion members 21 to 23 and on the outer peripheral side of the curved portion 2a, and is indicated by a one-dot chain line. The urea water F can be injected toward the surfaces 21a to 23a of the dispersion members 21 to 23.

The mixer 31 is a substantially disk-shaped member disposed adjacent to the downstream end of the dispersion members 21 to 23, and is perpendicular to the direction in which the exhaust gas flows in the straight pipe portion 2b. It is provided as follows. Moreover, in the site | part in which the mixer 31 is located, the straight piping part 2b is divided | segmented into the upstream piping part 2d and the downstream piping part 2e, and the outer peripheral part of the mixer 31 is hold | maintained among these.

As shown in FIG. 3 (a), a plurality of first fins 32a and a plurality of first fins 32a and a plurality of first fins 32a are bent at portions located inside the exhaust pipe 2 in the mixer 31 by bending a trapezoidal cut that is partially connected. Two fins 32b are formed. The mixer 31 has a plurality of openings 33 formed by bending the

fins

32 a and 32 b, and the exhaust gas flowing from the upstream side of the mixer 31 passes through these openings 33. Distributes downstream. Further, in the mixer 31 according to the present embodiment, a rectangular pipe member 35 (see FIG. 3b) is disposed on the upstream side corresponding to each opening 33, and the exhaust gas that has passed through the dispersion members 21 to 23 is disposed. However, the opening 33 is passed through the rectangular pipe member 35 as it is.

The first fin 32a and the second fin 32b are bent in directions opposite to each other, and the first fin 32a is bent so that the tip portion thereof faces the left side in FIG. On the other hand, the second fin 32b is bent so that the tip thereof faces the right side in FIG. In addition, the

fins

32a and 32b are arranged such that a row in which a plurality of first fins 32a are arranged in the left-right direction and a row in which a plurality of second fins 32b are arranged in the left-right direction are parallel to each other. It is arranged alternately one row at a time. In other words, the mixer 31 is a device that generates turbulent flow by inclining the flow of exhaust gas that passes through the first fin 32a and the second fin 32b in different directions, thereby mixing the fluid that passes therethrough. is there. Further, as shown in FIG. 3B, a pair of support portions 34 projecting to the upstream side are joined to the upstream surface 31 a of the mixer 31, and both sides of the dispersion member 21 are joined by these support portions 34. The part is supported.

Here, FIG. 4 shows a cross section of the straight pipe portion 2b at the portion where the dispersing members 21 to 23 are located. Note that the injection nozzle 5 of FIG. 4 is originally disposed in a portion not shown in FIG. 4 but is shown in the same cross section for convenience of explanation. As shown in FIG. 4, each of the dispersion members 21 to 23 has a width that substantially contacts the inner peripheral surface of the straight pipe portion 2b, and the inside of the straight pipe portion 2b is above the dispersion member 21 in FIG. Are divided into a region R1 on the right side, a region R2 between the dispersion member 21 and the dispersion member 22, a region R3 between the dispersion member 22 and the dispersion member 23, and a region R4 on the left side of the dispersion member 23. Yes. 4, the spray nozzle 5 sprays urea water F perpendicularly to the dispersion members 21 to 23.

That is, the urea water F injected from the injection nozzle 5 is dispersed in the regions R1 to R3 by colliding with the surfaces 21a to 23a of the dispersion members 21 to 23, but does not flow into the region R4. ing. On the other hand, the flow of the exhaust gas that has passed through the SCR catalyst 4 and the curved portion 2a (see FIG. 2) is divided by the dispersing members 21 to 23 so as to pass through all the regions R1 to R4. Further, the direction in which the dispersing members 21 to 23 divide the flow of exhaust gas corresponds to the direction in which the first fin 32a and the second fin 32b of the mixer 31 incline the flow of exhaust gas (see FIGS. 2 and 3). ing.

Here, as described above with reference to FIG. 2, since the dispersing members 21 to 23 and the mixer 31 are adjacent to each other, the urea water dispersed by colliding with the surfaces 21a to 23a of the dispersing members 21 to 23 is It is immediately supplied to the mixer 31 by the flow of the exhaust gas. On the other hand, when it is attempted to disperse the urea water only by the mixer 31 without using the dispersing members 21 to 23, in order to make the urea water distribution in the exhaust gas uniform, the urea water is applied to the entire surface of the mixer 31. It is necessary to make it collide. However, in order for the urea water F injected from the injection nozzle 5 to collide with the entire surface of the mixer 31, the urea water injection range between the injection nozzle 5 and the mixer 31 is widened so that the injection range of the urea water extends over the entire surface of the mixer 31. Therefore, it is necessary to make the straight pipe portion 2b longer.

That is, the exhaust gas aftertreatment device according to the present invention shortens the distance between the injection nozzle 5 and the mixer 31 by causing the urea water injected by the injection nozzle 5 to directly collide with the dispersion members 21 to 23 and disperse. It is. Further, the distance is further shortened by making the dispersing members 21 to 23 and the mixer 31 adjacent to each other. Accordingly, the distance between the oxidation catalyst 3 (see FIG. 1) and the SCR catalyst 4 is also shortened, so that the exhaust gas aftertreatment device can be miniaturized to improve the mountability on the vehicle. Further, since the apparatus is downsized, the temperature drop until the exhaust gas reaches the SCR catalyst 4 is suppressed, so that the NOx purification by the SCR catalyst 4 can be performed efficiently.

Next, the operation of the exhaust gas aftertreatment device according to Embodiment 1 of the present invention will be described.
As shown in FIG. 1, when the operation of the diesel engine 1 is started, the exhaust gas discharged from the exhaust pipe 2 flows through the inside of the exhaust pipe 2 and passes through the oxidation catalyst 3. The oxidation catalyst 3 oxidizes carbon monoxide (CO), hydrocarbon (HC), etc. contained in the exhaust gas passing therethrough, and at the same time oxidizes a part of nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ). Further, when the operation of the diesel engine 1 is started, the ECU 9 outputs a signal to the urea water addition system 7 and starts injection of urea water by the injection nozzle 5. The

NOx sensors

11 and 12 detect the NOx concentration on the upstream side and the downstream side of the SCR catalyst 4 as needed, and the ECU 9 controls the operation of the injection nozzle 5 based on these detection results.

As shown in FIG. 2, the exhaust gas that has passed through the oxidation catalyst 3 passes through the curved portion 2a of the exhaust pipe 2 and flows into the straight piping portion 2b, and is divided into regions R1 to R4 partitioned by the dispersion members 21 to 23. (See FIG. 4). Further, the urea water F sprayed from the spray nozzle 5 is atomized by colliding with the surfaces 21a to 23a of the dispersion members 21 to 23, and the atomized urea water passes through the regions R1 to R3 (see FIG. 4). Dispersed in the circulating exhaust gas. The urea water dispersed in the exhaust gas is hydrolyzed by the heat of the exhaust gas in the process of flowing downstream, thereby producing ammonia. Further, the dispersion members 21 to 23 are efficiently heated by the heat of the exhaust gas flowing through the inside of the exhaust pipe 2, and the hydrolysis of urea water is further promoted by the heat.

Here, as shown in FIG. 5, since the dispersion members 21 to 23 are arranged on the downstream side of the bending portion 2a, the exhaust gas reaching the dispersion members 21 to 23 is also generated as indicated by arrows A1 to A3. It circulates while curving. In such a case, the flow of exhaust gas is usually difficult to flow around the regions R11 to R13 indicated by the dotted lines around the surfaces 21a to 23a, so that the urea water atomized by colliding with the surfaces 21a to 23a is dispersed. It becomes difficult.

However, since the injection nozzle 5 injects the urea water F from the upstream side toward the surfaces 21a to 23a, the flow of the injected urea water F is indicated by arrows A1 to A3 as indicated by arrows B1 to B3. It impinges on the surfaces 21a-23a across the indicated exhaust gas flow diagonally. That is, even if the curved portion 2a is on the upstream side of the dispersion members 21 to 23, the flow of the exhaust gas can be generated in the regions R11 to R13 using the flow of the urea water F injected by the injection nozzle 5. Therefore, it is possible to efficiently disperse the urea water colliding with the surfaces 21a to 23a in the straight pipe portion 2b. That is, since the flow of the exhaust gas does not easily flow around the surfaces 21a to 23a of the dispersion members 21 to 23 arranged on the downstream side of the curved portion 2a, dispersibility is poor only by applying the urea water F normally. In the present embodiment, since the urea water F is injected from the upstream side toward the surfaces 21a to 23a to assist the flow of the exhaust gas, the dispersibility is good.

Further, since the exhaust gas flow is stronger on the outer peripheral side of the curved portion 2a than on the inner peripheral side, urea water is likely to be dispersed even if there is no dispersing member in the region R1 on the right side (that is, the outer peripheral side) in FIG. Therefore, in order to disperse the urea water uniformly, the dispersing members 21 to 23 are preferably arranged from the center to the left side (that is, the inner peripheral side) as shown in FIG. Moreover, since the outer peripheral side of the curved portion 2a usually has a larger mounting space than the inner peripheral side, it is convenient to dispose the injection nozzle 5.

Further, the dispersion members 21 to 23 have widths that substantially contact the inner peripheral surface of the straight pipe portion 2b (see FIG. 4), and urea water is not supplied to the region R4 farthest from the injection nozzle 5. The amount of urea water adhering to the inner peripheral surface of the straight piping portion 2b is reduced. Here, although the straight piping part 2b is heated by the exhaust gas which distribute | circulates the inside, the outer peripheral surface is cooled with external air. Therefore, for example, the temperature of the straight pipe portion 2b immediately after starting the diesel engine 1 (see FIG. 1) is lower than the temperature of the exhaust gas.

In this state, when urea water adheres to the inner peripheral surface of the straight pipe portion 2b, hydrolysis does not occur, the urea water moisture evaporates and urea remains, and the remaining urea remains in the inner peripheral surface of the straight pipe portion 2b. May be deposited on. Further, the accumulated urea does not reach the SCR catalyst 4 (see FIG. 2), and the amount of ammonia that is originally required is not supplied to the SCR catalyst 4, so it is necessary to increase the amount of urea water added.

However, in the exhaust gas aftertreatment device according to the present invention, the amount of urea water adhering to the inner peripheral surface of the straight pipe portion 2b is reduced by dividing the region R4 to which the urea water injected from the injection nozzle 5 is not supplied. Therefore, most of the injected urea water can be supplied to the SCR catalyst. In addition, since the dispersion members 21 to 23 are shorter in the direction of exhaust gas flow than the exhaust pipe 2 and have a small heat capacity, they are easily heated by the exhaust gas. Therefore, generation of ammonia from the urea water adhering to the dispersion members 21 to 23 is not hindered due to the low temperature of the exhaust pipe 2.

2, since the dispersing member 21 and the mixer 31 are arranged adjacent to each other, the urea water dispersed in the regions R1 to R3 is immediately supplied to the mixer 31 by the flow of the exhaust gas. On the other hand, the exhaust gas flowing through the region R4 is supplied to the mixer as it is without adding the urea water F. The exhaust gas and urea water flowing from the regions R1 to R3 and the exhaust gas flowing from the region R4 are mixed by the turbulent flow generated when passing through the plurality of

fins

32a and 32b of the mixer 31, thereby The urea water is uniformly mixed with the exhaust gas.

When the exhaust gas and ammonia that have passed through the mixer 31 are supplied to the SCR catalyst 4 in this way, the SCR catalyst 4 reacts with the ammonia and the exhaust gas to convert NOx contained in the exhaust gas into harmless nitrogen (N ₂ ). Reduce to water (H ₂ O). The dispersing members 21 to 23 are flat members and extend in parallel to the axial direction of the straight pipe portion 2b, so that NOx can be purified without increasing the pressure loss of the exhaust gas. it can.

The exhaust gas that has passed through the SCR catalyst 4 passes through a filter (not shown) provided on the downstream side of the SCR catalyst 4, and particulate matter contained in the exhaust gas is removed at that time. In addition, when exhaust gas contains surplus ammonia that has not passed through the SCR catalyst 4, a slip catalyst (not shown) provided on the downstream side of the filter removes surplus ammonia. To do. The exhaust gas that has passed through the slip catalyst is released into the atmosphere after noise is reduced inside a muffler (not shown).

As described above, the dispersion members 21 to 23 are provided between the curved portion 2a of the exhaust pipe 2 and the SCR catalyst 4, and the injection nozzle 5 is disposed at a portion where urea water can be injected toward the dispersion members 21 to 23. Therefore, the urea water atomized by colliding with the dispersing members 21 to 23 is dispersed in the exhaust pipe 2. In addition, since the mixer 31 is provided between the dispersing members 21 to 23 and the SCR catalyst 4, the urea water that collides with the dispersing members 21 to 23 and is dispersed by the mixer 31 is mixed with the exhaust gas by the mixer 31. To be supplied. That is, since the urea water can be preliminarily dispersed by the dispersing members 21 to 23, the injection nozzle 5 and the mixer 31 are used to widen the injection range of the urea water as in the case where the urea water is directly injected toward the mixer 31. There is no need to increase the distance between the two.

Further, since the exhaust gas that reaches the dispersion members 21 to 23 flows while being curved along the curved portion 2a, the exhaust gas normally flows in the regions R11 to R13 around the surfaces 21a to 23a of the dispersion members 21 to 23. Thus, the exhaust gas flow hardly occurs. Here, since the injection nozzle 5 injects urea water from the upstream side toward the surfaces 21a to 23a, the flow of the injected urea water obliquely crosses the exhaust gas flowing while curving and collides with the surfaces 21a to 23a. To do. In other words, since the flow of the exhaust gas can be generated in the regions R11 to R31 by the flow of the urea water injected from the injection nozzle 5, the urea water colliding with the dispersion members 21 to 23 can be efficiently dispersed. . Therefore, in the exhaust gas aftertreatment device having the exhaust pipe 2 including the curved portion 2a, it is possible to reduce the size while uniformly dispersing the urea water in the exhaust gas.

Since the dispersing members 21 to 23 and the mixer 31 are arranged adjacent to each other to shorten the distance between them, the exhaust gas aftertreatment device can be further downsized. In addition, since the urea water dispersed by the dispersion members 21 to 23 immediately passes through the mixer 31, the urea water can be efficiently mixed with the exhaust gas.

Further, since the dispersing members 21 to 23 and the mixer 31 are provided in the straight piping portion 2b extending linearly, and the dispersing members 21 to 23 extend along the axial direction of the straight piping portion 2b, without increasing pressure loss. The urea water can be supplied to the mixer 31.

Furthermore, since the exhaust gas aftertreatment device is configured to include the plurality of dispersion members 21 to 23, more urea water can collide with the dispersion members 21 to 23, and the urea water is efficiently dispersed.

Embodiment 2. FIG.
Next, an exhaust gas aftertreatment device according to Embodiment 2 of the present invention will be described. In the exhaust gas aftertreatment device according to the second embodiment, the dimensional regulations described below are added to the exhaust pipe 2 and the mixer 31 of the exhaust gas aftertreatment device according to the first embodiment.

As shown in FIG. 6, the diameter of the SCR catalyst 4 located on the downstream side of the mixer 31 is larger than the diameter of the downstream piping part 2e, and the downstream piping part 2e and the SCR catalyst 4 are directed from the upstream side toward the downstream side. Are connected via a tapered pipe portion 2c formed so as to spread in a tapered shape. That is, the mixer 31 and the SCR catalyst 4 are sequentially connected via the downstream piping portion 2e and the tapered piping portion 2c, which are a part of the straight piping portion 2b extending linearly.

As described in the first embodiment, the bent directions of the first fin 32a and the second fin 32b are opposite to each other, but the angle is a common angle α. That is, the mixer 31 inclines the flow of the exhaust gas before passing through the mixer 31 by the first fin 32a and the second fin 32b by an angle α in the left-right direction opposite to each other.

The angle α at which the first fin 32a and the second fin 32b are bent in the mixer 31, that is, the angle α at which the

fins

32a and 32b incline the flow of the exhaust gas is set to 45 °. Moreover, the internal diameter D of the downstream piping part 2e which connects the mixer 31 and the taper piping part 2c is set to 66 mm. In this way, in the exhaust gas aftertreatment device in which the angle α = 45 ° and the inner diameter D = 66 mm, the length L of the downstream pipe portion 2e is defined according to the angle α and the inner diameter D, and the following ( 1) It is set to satisfy the equation.
D / 2 × cotα ≦ L ≦ 3/2 × D × cotα (1)
That is, when α = 45 ° and the inner diameter D = 66 mm, the range of the length L is 33 (mm) ≦ L ≦ 99 (mm).

When the angle α is 45 °, that is, when cot α = 1 in the above equation (1), the length L of the downstream pipe portion 2e eventually satisfies the following equation (2). Set to
2 / D ≦ L ≦ 3/2 × D (2)
In the exhaust gas aftertreatment device according to the second embodiment, the length L of the downstream pipe portion 2e is set to 43 mm that satisfies the expressions (1) and (2). Note that the slope β of the taper pipe portion 2c spreading toward the downstream side, that is, the angle β at which the taper pipe portion 2c spreads with respect to the axial direction of the downstream pipe portion 2e is smaller than the angle α = 45 °. Yes. Other configurations are the same as those in the first embodiment.

In the exhaust gas aftertreatment device configured as described above, in order to efficiently reduce NOx by the SCR catalyst 4, it is necessary to supply ammonia to the entire surface of the SCR catalyst 4 in a uniform distribution state. Become. For that purpose, it is necessary to uniformly disperse ammonia in the exhaust gas and to diffuse the exhaust gas in the tapered pipe portion 2c. Here, as shown in FIG. 3A, the first fin 32a and the second fin 32b of the mixer 31 are bent in the left and right directions opposite to each other, and the flow of exhaust gas passing therethrough. Tilt left and right. The

fins

32a and 32b are arranged such that a plurality of first fins 32a are arranged in the left-right direction and a plurality of second fins 32b are arranged in the left-right direction. They are arranged one by one alternately so as to be parallel.

Therefore, as shown in FIG. 7, the flow of exhaust gas inclined to the left side by the row of the first fins 32a (inside the downstream piping portion 2e on the downstream side of the mixer 31 (see FIG. 6)) ( An arrow B1) and an exhaust gas flow inclined to the right by the row of the second fins 32b (see the arrow B2) are alternately adjacent to each other. Moreover, since the downstream side piping part 2e is cylindrical, the flow along the circumferential direction of the downstream side piping part 2e (see arrow B3) flows in the exhaust gas that has collided with the inner peripheral surface 2f of the downstream side piping part 2e. Given. That is, out of the exhaust gas flowing through the mixer 31 and flowing into the downstream pipe portion 2e, the exhaust gas that has collided with the inner peripheral surface 2f has a cross section perpendicular to the axial direction of the downstream pipe portion 2e. A circulating flow is provided. Thereby, it becomes possible to disperse ammonia efficiently with respect to the exhaust gas flowing through the downstream side piping part 2e.

Further, as shown in FIG. 8, the exhaust gas that has passed through the mixer 31 is provided with a flow inclined at an angle α in the left-right direction by the first fin 32a and the second fin 32b, as indicated by an arrow C1. Moreover, the exhaust gas that has collided with the inner peripheral surface 2f of the downstream side piping part 2e goes straight along the axial direction of the downstream side piping part 2e. Here, the timing at which the exhaust gas that has passed through the first fin 32a and the second fin 32b collides with the inner peripheral surface 2f of the downstream pipe portion 2e varies depending on the positions of the

fins

32a and 32b. The flow of exhaust gas along the axial direction and the flow of exhaust gas inclined at an angle α coexist in the downstream side piping part 2e.

More specifically, in the case of the first fin 32a, the exhaust gas that has passed through the first fin 32a located on the leftmost side collides with the inner peripheral surface 2f at the earliest timing (see arrow C1). The timing of the collision is delayed as the position of the fin 32a becomes the right side (see arrow C2). Further, when the position of the first fin 32a is further on the right side, the exhaust gas that has passed does not collide with the inner peripheral surface 2f and flows in a direction (see arrow C3) directly flowing into the tapered pipe portion 2c. The second fin 32b is the same except that the direction is reversed. Therefore, the exhaust gas flow (see arrows C1 and C2) along the axial direction of the downstream pipe portion 2e collides with the exhaust gas flow (see arrow C3) inclined with respect to the axial direction, and the angle of the flow α is gradually decreased (see arrow C4).

That is, the flow angle of the exhaust gas flowing through the downstream pipe portion 2e and flowing into the tapered pipe portion 2c is the angle α at which the first fin 32a and the second fin 32b tilt the flow of the exhaust gas, and the downstream side When the pipe portion 2e has an inner diameter D and a distance L (see FIG. 6) and these satisfy the above-described expressions (1) and (2), the flow of exhaust gas along the axial direction (arrow) C1, C2) and the flow of exhaust gas inclined with respect to the axial direction (arrow C3) are balanced. Since the angle β of the gradient of the tapered pipe portion 2c is smaller than the angle α, a flow substantially along the angle β is given to the exhaust gas that has passed through the downstream side pipe portion 2e. Accordingly, since the ammonia dispersed in the exhaust gas in the downstream pipe portion 2e is diffused along the gradient of the taper pipe portion 2c, the ammonia can be supplied to the SCR catalyst 4 in a uniform distribution state. It becomes.

Here, when the angle α is 45 °, the inner diameter D is 66 mm, and the length L is changed, the transition of the distribution state of ammonia supplied to the SCR catalyst 4, the transition of the so-called in-plane uniformity is measured. Is shown in FIG. The exhaust gas flow rate was 52 (g / s), and the exhaust gas temperature was 423 (° C.). In this case, according to the exhaust gas aftertreatment device according to the second embodiment, the preferred range of the length L is
33 (mm) ≤ L ≤ 99 (mm)
In such a range, the CV value can be made less than 10%. FIG. 9 shows the CV value (variation coefficient: number obtained by dividing the standard deviation by the average × 100), which is one of the indices indicating the in-plane uniformity, with the length L of the downstream pipe portion 2e as the horizontal axis. It is the graph which made the vertical axis | shaft. Further, the CV value becomes zero when the distribution state of ammonia supplied to the SCR catalyst 4 becomes uniform, and increases as the distribution state becomes non-uniform.

As shown in FIG. 9, when the length L of the downstream pipe portion 2e is less than about 30 (mm), the CV value is rapidly increased. This is because the length L of the downstream pipe portion 2e is too short, so that the exhaust gas flows into the tapered pipe portion 2c before ammonia is sufficiently dispersed inside the downstream pipe portion 2e. That is, the flow of exhaust gas tilted with respect to the axial direction (arrow C3 in FIG. 8) becomes too strong, resulting in insufficient dispersion.

On the other hand, when the length L of the downstream pipe portion 2e exceeds about 50 (mm), the CV value gradually increases as the length L increases. This is because the flow in the direction along the axial direction of the downstream pipe portion 2e (see arrows C1 and C2 in FIG. 8) becomes too strong as the length L increases, so that the exhaust gas flowing into the tapered pipe portion 2c. Is not diffused along the taper shape but goes straight as it is and is supplied only to the vicinity of the center of the SCR catalyst 4. As described above, when the angle α, the inner diameter D, and the length L satisfy the above-described formulas (1) and (2), ammonia is supplied to the SCR catalyst 4 in a uniform distribution state from FIG. Can also be confirmed.

Even when the flow rate and flow rate of the exhaust gas change, the flow rate and flow rate of the flows indicated by arrows C1 to C4 shown in FIG. 8 change at the same rate, so the result is the same as that shown in FIG. It becomes a trend.

As described above, in the exhaust gas aftertreatment device in which the mixer 31 and the SCR catalyst 4 are connected to each other via the downstream pipe portion 2e and the taper pipe portion 2c, the first fin 32a and the second fin 32a of the mixer 31 are connected. When the angle at which the flow of the exhaust gas passing through the fin 32b is inclined is α, the inner diameter of the downstream pipe portion 2e is D, and the length is L,
D / 2 × cotα ≦ L ≦ 3/2 × D × cotα
When it is configured to satisfy the condition, a flow along the gradient of the tapered pipe portion 2c can be generated for the exhaust gas that has passed through the downstream side pipe portion 2e and has flowed into the tapered pipe portion 2c. Therefore, in addition to obtaining the same effect as in the first embodiment, ammonia can be supplied to the SCR catalyst 4 in a uniform distribution state.

Further, in the mixer 31, since the rows in which the plurality of first fins 32a are arranged and the rows in which the plurality of second fins 32b are arranged are alternately arranged one by one, in the downstream side piping section 2e, Exhaust gas flows in directions different from each other occur alternately and ammonia is efficiently dispersed in the exhaust gas. Furthermore, since the downstream side piping part 2e is cylindrical, the flow along the circumferential direction is given to the exhaust gas that has passed through the mixer 31 and collided with the inner peripheral surface 2f of the downstream side piping part 2e, and ammonia is more efficient. It is often dispersed in exhaust gas.

Although the exhaust gas aftertreatment device according to

Embodiments

1 and 2 is configured to include three dispersing members, the number of dispersing members is not limited to three. The number of dispersing members can be appropriately changed mainly depending on layout factors such as the position of the curved portion and the inner diameter of the exhaust pipe, and includes three members including a single dispersing member. It is possible to change to a number other than.

In the first and second embodiments, the dispersive member and the mixer are disposed adjacent to each other. However, they can be disposed apart from each other. Although the length of the exhaust pipe is increased by separating the dispersing member and the mixer, the effect that the urea water can be dispersed in advance on the upstream side of the mixer can be obtained without change.

Although the respective dispersion members in the first and second embodiments have different lengths and the longest dispersion member is disposed at a position far from the injection nozzle, the present invention is not limited to such a configuration. As long as it is possible to disperse the urea water sprayed from the spray nozzle, it may be dispersed due to layout factors when all the dispersive members have the same length or as the distance from the spray nozzle decreases. The length of the member may become longer.

In addition, each dispersion member in the first and second embodiments is configured to have a width that substantially contacts the inner peripheral surface of the exhaust pipe, but is configured to be separated from the inner peripheral surface and supported only by the mixer. It is also possible. In this case, since the exhaust pipe having a relatively low temperature and the dispersion member are separated from each other by being in contact with the outside air, it is possible to promote the hydrolysis of urea water by keeping the temperature of the dispersion member at a high temperature. Become.

Further, the mixer 31 in the first and second embodiments is configured to have the rectangular pipe member 35 corresponding to the opening 33, but may be configured by omitting the rectangular pipe member 35. . In addition, the mixer 31 and the dispersion members 21 to 23 may be arranged apart from each other, but the mixer 31 and the dispersion member 21 are such that the exhaust gas that has passed through the dispersion members 21 to 23 passes through the opening 33 as it is. ˜23 are adjacent to each other, the exhaust gas can be guided to the mixer 31 with a controlled flow of exhaust gas, so that improvement in dispersibility can be expected and miniaturization can be achieved.

Claims

An exhaust pipe through which exhaust gas discharged from the internal combustion engine flows and has a curved portion that curves the direction in which the exhaust gas flows;
A reducing agent supply device for injecting a reducing agent into the exhaust pipe;
An exhaust gas aftertreatment device, which is disposed downstream of the reducing agent supply device and the bending portion, and includes a reduction catalyst that purifies the exhaust gas by reacting the exhaust gas and the reducing agent,
A plate-like dispersion member disposed between the curved portion and the reduction catalyst and provided so that one surface faces the outer peripheral side of the curved portion;
A mixing means disposed between the dispersion member and the reduction catalyst, and further mixing the exhaust gas and the reducing agent;
The reducing agent injection device is an exhaust gas post-processing device that is disposed at a site upstream of the dispersing member and capable of injecting the reducing agent toward the one surface of the dispersing member.
The exhaust gas aftertreatment device according to claim 1, wherein the dispersing member and the mixing means are disposed adjacent to each other.
The exhaust pipe extends straight and has a straight pipe part between the curved part and the reduction catalyst in which the dispersion member and the mixing means are arranged.
The exhaust gas aftertreatment device according to claim 1 or 2, wherein the dispersion member extends in parallel to an axial direction of the straight pipe portion.
The exhaust gas aftertreatment device according to any one of claims 1 to 3, wherein there are a plurality of dispersion members.
The mixing means includes a plurality of first fins and a plurality of second fins that are arranged so as to be parallel to each other and that incline the flow of the exhaust gas passing therethrough at a predetermined angle that is opposite to each other. And
The mixing means and the reduction catalyst are sequentially connected through a part of the straight piping portion and a tapered piping portion formed so as to widen from the upstream side to the downstream side,
When the angle is α, the inner diameter of the straight piping portion is D, and the length of the straight piping portion from the mixing means to the tapered piping portion is L,
D / 2 × cotα ≦ L ≦ 3/2 × D × cotα
The exhaust gas aftertreatment device according to claim 3 or 4, satisfying
The exhaust gas aftertreatment according to claim 5, wherein the mixing unit includes a row in which a plurality of the first fins are arranged and a row in which the plurality of second fins are arranged alternately. apparatus.
The exhaust gas aftertreatment device according to any one of claims 3 to 6, wherein the straight pipe portion is cylindrical.
The exhaust gas aftertreatment device according to any one of claims 5 to 7, wherein a gradient in which the tapered pipe portion spreads is smaller than the angle α.
The exhaust gas aftertreatment device according to any one of claims 5 to 8, wherein the angle α is 45 °.